One other framework to consider: Matter.js —Demo: Easy Physics Sandbox in JavaScript.
The Physics
Gravity is hard. That's because gravity is curved spacetime, and we can only make 2d representations of this warping that happens in the third dimension.
On the other hand -- moving an element at a consistent 9.8 m/s^2 in a linear direction towards one direction, that's actually not too hard to implement.
The CSS Solution
All we really need is transition: all 1s linear; to control the speed of the animation, margin-top to animate the element moving downward, and transition-timing-function with a cubic-bezier that's fairly representative of 9.8 m/s^2.
The Demo
document.addEventListener('DOMContentLoaded', function(event) { document.getElementById('drop').addEventListener('click', function(ev) { div = document.createElement('div'); div.classList.add('gravity-affected-object'); image = document.createElement('img'); image.src = 'https://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Red_Apple.jpg/640px-Red_Apple.jpg'; image.width = 100; image.classList.add('gravity-affected-object'); div.style.position = 'absolute'; div.style.left = '50%'; div.appendChild(image); document.getElementById('page-top').appendChild(div); setTimeout(function() { div.style.marginTop = '1000px'; }, 100); });});.gravity-affected-object { transition: all 1s linear; transition-timing-function: cubic-bezier(0.33333, 0, 0.66667, 0.33333); z-index: -5000;}<div id="page-top"></div><button id="drop">Drop</button>